Add the pyhepmc package to the stack

[jmcarcell]

@BrieucF
This lets me do import pyhepmc without issues

[BrieucF]

Hi Juan, thanks! I realize that this is the version from scikit-learn, the Python bindings from HepMC3 are retrieved with import pyHepMC3 which, as you spotted, only works after

export PYTHONPATH=/cvmfs/sw-nightlies.hsf.org/key4hep/releases/2024-09-21/x86_64-almalinux9-gcc14.2.0-opt/hepmc3/3.3.0-c2oek4/lib/python3.11/site-packages:$PYTHONPATH

can we also fix this?

[jmcarcell]

Yes, that's independent of this. So is this package not needed and by pyhepmc you meant the python bindings of HepMC3 instead of the scikit package?

[BrieucF]

I have tried both pyhepmc and pyHepMC3, I think I will go for pyHepMC3 for the final solution but I can't say for sure now